1. Field of the Invention
The present invention relates to a source driver, and more particularly, to a source driver which does not include any P-type digital-to-analog converter.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is a diagram illustrating a prior art source driver 100. As shown in FIG. 1, the source driver 100 includes two adjacent channels 110 and 120, where the channel 110 includes a P-type digital-to-analog converter (PDAC) 112, an N-type digital-to-analog converter (NDAC) 114 and a buffer amplifier 116, and the channel 120 includes a PDAC 122, an NDAC 124 and a buffer amplifier 126. The PDAC is a digital-to-analog converter whose switches are all implemented by P-type Metal-Oxide-Semiconductors (PMOS), and the NDAC is a digital-to-analog converter whose switches are all implemented by N-type Metal-Oxide-Semiconductors (NMOS). In addition, multiplexers 102, 104 and 106 are respectively coupled between the elements in the two channels 110 and 120, and are used for switching the received signals.
In the operations of the source driver 100, taking the channel 100 as an example and assuming that a supply voltage of the source driver is 18V, the PDAC 112 receives gamma voltages ranging from 9V to 18 V to prevent break-down between the source/drain region and the substrate of the PMOS. The NDAC 114 receives gamma voltages ranging from 0V to 9V to prevent break-down between the source/drain region and the substrate of the NMOS. Then, the PDAC 112 or the NDAC 114 selects one of the gamma voltages according to the input signal A0-AN−1 or B0-BN−1, and outputs the selected gamma voltage. One of the buffer amplifiers 116 and 126 receives the output signal generated from the PDAC 112 or the NDAC 114 and outputs the buffered output signal Vout_1 or Vout_2.
In addition, because each channel included in the prior art source driver 100 has a PDAC and an NDAC, the source driver 100 requires a large chip area due to the design rule of the PDAC and NDAC, causing higher cost of the source driver 100. Furthermore, each buffer amplifier included in the prior art source driver 100 needs to be implemented by a rail-to-rail operational amplifier whose deviation of a head/tail voltage is great, causing poor quality of the amplified signal.